[support] Page not found errors Drupal 8

Learning how to create modules and forms I followed the tutorial exactly but get Page not found error. Also it seems the YAML syntax has changed within Drupal 8, Where |demo.demo:| |||path: '/demo'| |||defaults:| |||_content: '\Drupal\demo\Controller\DemoController::demo'| |||_title: 'Demo'| |||requirements:| |||_permission: 'access content'

is now- | |demo.demo:| |||path: '/demo'| |||defaults:| |||- content: '\Drupal\demo\Controller\DemoController::demo'| |||- title: 'Demo' and | |||requirements:| |||- permission: 'access content' or any other permission causes an error when the caches are cleared.

Can someone please advise what's going on here please? Thanks Roger |